Turtles hide in their shells when they are scared. The hard exterior protects them from enemies. However, recent studies say that the ancestors of these animals used their retractable necks to catch food. It’s likely that it later evolved into a defense mechanism to protect the turtles from danger.
Let’s take a closer look at this now.
A Closer Look At The Shell Structure Of Turtles
The shell of a turtle is its home. It is a protective structure that is made up of hard bone.
This hard armor houses the sensitive parts of the animal’s body.
Although other creatures like snails, hermit crabs, and mollusks also have shells, the turtle’s shell is unique.
A turtle’s shell is attached to its spine and rib cage.
It is a permanent fixture that is present from the time the animal is born.
It is integrated with the body, and the animal cannot survive without its shell.
The turtle shell consists of two parts. The upper portion is called the carapace, and the lower half is called the plastron.
The ribs and vertebrae fuse to form the carapace.
The clavicles, bones between the clavicles, and part of the ribs fuse to form the plastron.
The carapace and plastron are attached by a bony structure along the side called the bridge.
Some turtle shells also have a moveable joint called a hinge. The hinge is attached to the carapace and plastron.
When the turtle retracts into the shell, the hinge tightens and brings the carapace and plastron together.
Thus, by reducing the gap between the carapace and plastron, the crevices where the head and limbs belong are tightened.
So, an attacking animal cannot pry its claws or nails into these spaces.
The shell of a turtle is a living bone. It has nerve endings and a continuous blood supply. So, any injury to the shell is painful.
The shell also needs a continuous supply of calcium and minerals to stay healthy.
Calcium deficiencies can cause distorted, weak, and brittle bones that are prone to breakage and injury.
Turtle shells are also susceptible to various diseases and infections since they are living structures.
What Does The Turtle’s Shell Do?
If you pity turtles for hauling their heavy shells everywhere, you should know that there are several benefits of doing their shell.
Firstly, the shell offers protection to the animal.
You may already know that turtles are one of the slowest creatures out there.
In the wild, speed plays an important role in determining an animal’s chances of survival.
Slow animals are vulnerable as they are easily chased and attacked.
However, a turtle has an advantage because of its shell.
Though they cannot run from their enemies, turtles can almost instantly pull themselves into their shells.
The attacking animal will not find it easy to get past the thick, bony shell and get to the soft, meaty part of the turtle.
Hence, they will most likely leave the turtle alone.
Now, did you know that the turtle’s shell is not impervious to feeling? A turtle’s shell is made of living bone.
It has several nerve endings, and they are sensitive to pressure. So, if you scratch a turtle on its shell, the animal can feel it.
When the shell is wounded, the turtle will be in pain. That is why an injured shell takes a long time to heal.
A cracked or broken shell can badly affect the turtle, causing serious injury, paralysis, or even death.
Which Turtles Hide In Their Shells?
Not all turtles can completely retract their head and limbs into their shells.
It depends on the species, the structure of its shell, and environmental conditions.
Most tortoises and land turtles fully withdraw into their shells. When the animal conceals itself, only the shell is usually visible.
Although there are gaps where the head and limbs belong, predators cannot usually use them to gain access to the animal within it.
It is why most freshwater turtles use their shells as their armor to stay safe from predators.
Now, aquatic turtles do not have this special quality. Sea turtles, for instance, cannot withdraw into their shells like land turtles.
They must swim or hide to escape from enemies and threats.
Why Can’t Sea Turtles Hide In Their Shells?
The physiological make-up of sea turtles differs from those of freshwater and land turtles.
These animals have flippers instead of limbs.
Flippers are paddle-like structures with fused limbs. They help the turtles move and navigate the depths of oceans.
Another difference is in the structure of the shells. Land turtles have rounded shells.
Due to their shape, the shell offers more space for the turtle’s head and limbs.
On the other hand, sea turtles don’t have enough space in their shells to retract their limbs and head.
This is because their muscles have to be large and strong for swimming.
These muscles take up all the space inside the shell, thus not leaving much space to retract their limbs.
If sea turtles had pockets of cavity to retract their limbs, it would cause considerable drag while swimming, resulting in much slower movement through the water.
Additionally, sea turtles’ flippers are designed to be permanently outside the shell.
Their shells are better adapted for swimming than concealing the turtle’s body.
Contradictory Scientific Evidence About The Purpose Of A Turtle’s Shell
We just saw that turtles today use their shell as a defense mechanism.
Interestingly, scientific studies suggest that this is not what nature originally designed them for.
Now, turtles are classified into two categories based on how they retract their necks.
- Pleurodires: These turtles turn their heads sideways before pulling them back into their shells.
- Cryptodires: These turtles can pull their heads straight into their shells.
Studies on the fossil of an extinct turtle called the Platychelys Oberndorferi led to the stunning discovery of the original purpose of a turtle’s retractable neck.
Based on previous evidence, this turtle was originally classified as a Pleurodire turtle, and it had sharp protrusions on its shell.
However, a fossil of the Platychelys was discovered in recent years.
These skeletal remains of the animal suggest that it is a Cryptodire.
So, this animal would have been able to pull its head into the shell directly.
Now, the interesting fact was that it could only partially withdraw the head.
With part of the head exposed, this turtle would be vulnerable to predators.
In this case, the shell would not offer any protective benefits.
So, the presence of the shell indicated that its purpose was not protection.
This discovery led scientists to rethink the theory of the shells having evolved as a defensive mechanism for turtles.
The only plausible explanation was that the retractive capability was linked to its ability to catch food.
So, this turtle used its ability to retract into the shell to hide from prey and catch it unaware.
The behavior of certain varieties of turtles like the Mata Mata turtles of New Zealand and North American snapping turtles support this evidence.
These animals use their retractable necks for hunting.
They conceal themselves within their shells while waiting for their prey.
When small fish or crustaceans appear, they thrust their necks forward to catch them.
This sudden and forceful action clubbed with the powerful bite of its jaw kills the prey instantly.